Radiographic images captured by using radiation, represented by X-ray images, are widely used for the purpose of disease diagnosis and the like. These radiographic images for medical use are conventionally captured by using screen films. However, there has been developed a CR (Computed Radiography) apparatus which uses a stimulable phosphor sheet for digitalizing a radiographic image, and recently, there has been developed a radiographic image capturing apparatus which detects emitted radiation with radiation detection elements such as photodiodes (photoelectric conversion elements) to obtain the emitted radiation as digital image data.
Such type of radiographic image capturing apparatus is know as FPD (Flat panel Detector) and it has been conventionally developed as a so-called specialized machine which is formed integrally with a supporting platform or the like (for example, see patent documents 1 and 2). Further, in recent years, there has developed a portable radiographic image capturing apparatus in which radiation detection elements and the like are housed in a housing so as to be able to carry around and such portable radiographic image capturing apparatus has been utilized (for example, see patent documents 3 and 4).
As for radiographic image capturing apparatus, there is known a so-called direct type radiographic image capturing apparatus which generates electric charges with detection elements according to radiation doses such as emitted X-rays or the like and converts the electric charges into electric signals and a so-called indirect type radiographic image capturing apparatus which converts emitted radiation into electromagnetic waves of other wave length such as visible light or the like by a scintillator or the like and thereafter generates electric charges with photoelectric conversion elements such as photodiodes according to energy of the electromagnetic waves which are converted and emitted and converts the generated electric charges into electric signals. Here, in the present invention, detection elements in such direct type radiographic image capturing apparatus and photoelectric conversion elements in such indirect type radiographic image capturing apparatus are called radiation detection elements all together.
In patent documents 5 and 6, there are suggested radiographic image processing apparatuses and the like for generating radiographic images without unevenness by removing unevenness that occurs in radiographic images from radiographic images obtained with a conventional CR apparatus. In such radiographic image processing apparatuses and the like, by extracting unevenness components from a captured radiographic image and removing the extracted unevenness components from the original radiographic image, a radiographic image without unevenness can be generated.
In case of a CR apparatus, radiographic image capturing is carried out by emitting radiation onto a plate or the like including a stimulable phosphor sheet layer via a subject and the plate or the like is conveyed to a radiographic image reading apparatus so that a radiographic image is to be read out from the plate in the radiographic image reading apparatus.
At that time, as shown in FIG. 26, a laser beam output from a laser diode 101 is made to be parallel light by a collimator lens 102, a part of the parallel light reflects off a beam splitter 103 to be sent to a detector 104 and the monitoring result by the detector 104 is fed back to a laser drive circuit 105 so that the laser output from the laser diode 101 is adjusted in the radiographic image reading apparatus 100, for example.
Further, most part of the parallel light is refracted by an imaging lens 106 formed of a cylindrical lens and reflects off the mirror surface of a polygon mirror 107 and the reflection light is emitted onto the image surface of the plate P via a fθ lens 108 and a cylindrical mirror 109. At that time, by the polygon mirror 109 rotating, the laser beam which enters the image surface of the plate P travels in the main scanning direction X on the image surface as an excitation light and scans the image surface along the reading line Z.
When the laser beam which is excitation light enters the image surface of the plate P, radiation energy accumulated at a position in the stimulable phosphor layer of the plate P where laser beam enters is emitted as fluorescence. Then, the emitted fluorescence goes through a light-guiding tube 110a of a light concentrating device 110 to be concentrated at the light concentrating device 110 and the concentrated fluorescence is guided to a photomultiplier or a photodiode 111. The photodiode 111 or the like responds to the concentrated fluorescence and outputs output current.
In such way, pieces of image data of individual pixels on the plate P are obtained. Here, sub-scanning direction Y is the direction orthogonal to the main scanning direction X, and the plate P is subjected to scanning by the laser beam which is excitation light as described above while gradually moving in the sub-scanning direction Y. Thereby, pieces of image data of individual pixels on the plate P are read in two dimensional manner, and image data is read.
For example, in the radiographic image processing apparatus described in patent document 6, the pieces of read image data are arranged in two dimensional manner and the pieces of read image data are divided in strip-shaped areas Sa extending in the sub-scanning direction Y, for example, to obtain image data distribution of pixels aligned in the sub-scanning direction Y for each strip-shaped region Sa as shown in FIG. 27. Further, there is suggested to generate a radiographic image p without unevenness by performing high-pass filter processing or low-pass filter processing on the image data distribution to extract unevenness components in the original radiographic image p and remove the extracted unevenness components from the original radiographic image p.
Unevenness that occurs in the radiographic image p captured with a CR apparatus mainly occurs due to physical vibration of each member of the radiographic image reading apparatus 100, such as the polygon mirror 107 of the radiographic image reading apparatus 100 vibrating when it rotates and the cylindrical mirror 109 vibrating.
In view of the above, when the invention described in patent document 6 is to be applied, each member of the radiographic image reading apparatus 100 is adjusted so that cycles of vibration of each member occurs in a high-frequency side, for example, in most cases. By configuring the radiographic image reading apparatus 100 as described above, cycles of unevenness components that occur in a radiographic image p can be in the high-frequency side, for example.
Further, in image data where internal organs, bones and the like of a human body are captured, image data distribution appears more in a low-frequency side (that is, in long cycle side). Therefore, by performing high-pass filter processing, for example, on the image data distribution, unevenness components remain and image data components where internal organs, bones and the like of a human body are captured are cut off. Thus, in such case, only the unevenness components can be extracted from the radiographic image p by the high-pass filter processing.